I. Field of the Invention
The present invention relates to a magnetic recording and/or reproducing apparatus, and more specifically to apparatus for returning the magnetic head of the recording and/or reproducing apparatus to the zero track position of a magnetic disk.
II. Background Information
Magnetic recording and/or reproducing apparatus, for magnetic flexible (floppy) disks or magnetic diskettes (which hereinafter will also be referred to as floppy disks) which have been used as external data storage devices for information equipment are provided with a stop element called a "stopper" for mechanically preventing a magnetic head used in transferring data between information equipment and magnetic disks from moving in a radially outward direction beyond a reference or zero track (the track of a disk which is the outermost track radially within an available range).
Conventional magnetic recording and/or reproducing apparatus include a flexible disk controller and a flexible disk drive (or drives). The flexible disk controller (FDC) controls the flexible disk drive (FDD) which initially sets the position of a magnetic head of the FDD radially inside of the zero track position of a disk. After the apparatus is powered on, and prior to the transfer of data, an operation is performed allowing the magnetic head to move radially outward in response to a command signal. The magnetic head is thereby moved (actually, returned) to the zero track position of the disk.
The FDD receives the command for moving the magnetic head from the FDC. The FDD operates in the manner described below.
A control circuit (e.g., a microprocessor) for controlling mechanical and electrical systems of internal units assembled in the FDD operates, after the apparatus is powered on, to move a carriage on which the magnetic head is mounted to the zero track position of the disks of the FDD.
In the event that the initial position of the magnetic head is actually located radially outward of the zero track position for any reason, the following will occur.
Since, as shown in FIG. 4, output from a track zero position sensor and an excitation condition of a stepping motor in regard to the minus four (-4) track position (the -4 track being a disk track radially outward of the zero track) are the same as those in regard to the zero track, the FDC erroneously judges the -4 track as the zero track, and attempts to effect a control to move the magnetic head to the position of the minus four (-4) track.
There is a possibility that such an erroneously movement of the magnetic head results in the FDD being out of order. For preventing this out of order condition, conventional FDDs are provided with a stopper in the vicinity of the minus two (-2) track which is located radially inside of the minus four (-4) track.
The provision of such a stopper can prevent the magnetic head from moving toward a track positioned radially outward of the zero track. Accordingly, by exciting the stepping motor at the time when the magnetic head has been stopped to allow the excitation condition of the stepping motor to be in correspondence with that of the zero track (H.multidot.H condition as shown in FIG. 4), the magnetic head is made to return to the true zero track position. The conventional FDD necessarily requires a stopper in order to accomplish return of the magnetic head to the zero track in a stabilized manner.
In recent years, there has been developed, for use in magnetic recording and/or reproducing apparatus, an automatic return-to-zero (ARTZ) system for returning a magnetic head to the zero track position of a disk. The ARTZ system does not necessitate the provision of a stopper as previously mentioned, and therefore results in a reduction of the number of steps and cost of manufacturing recording and/or reproducing apparatus.
The operation of returning the magnetic head to the zero track position in accordance with this system is effected as described below.
Initially, after the apparatus is powered on, an internal controller (internal to the FDD) becomes operative to detect an output of a track zero position sensor. In the case where the magnetic head is positioned at a track radially inward of the zero track and the track position sensor, has an output of a high level (see FIG. 4), the internal controller of the FDD becomes operative to move the magnetic head toward the radially outward direction, and stops the movement of the magnetic head upon recognition of the position thereof on the basis of an output from the track position sensor and an excitation condition of a stepping motor.
On the other hand, in the case where the magnetic head is positioned at a track which is radially outside of the zero track (including a radially inside track extremely close to the zero track) and the track zero position sensor has an output of low level, the internal controller becomes operative to move the magnetic head in a radially inward direction until an output from the track position sensor shifts to the high level, thereafter moving the magnetic head in a radially outward direction and stopping the movement of the magnetic head upon recognition of the position thereof on the basis of an output from the track position sensor and the excitation condition of the stepping motor in the same manner stated above.
Thus, in accordance with the above-mentioned ARTZ system, there is no possibility that the magnetic head will attempt to return to the zero track by moving in a direction radially outward beyond the zero track regardless of the initial position of the magnetic head. Because no possibility of erroneous movement exists, there is no need for the provision of a stopper.
There is a problem however, when an FDD having the above-mentioned ARTZ system is utilized in connection with one of the recently developed battery-driven portable computers. Namely, when power is on, the internal controller of the FDD becomes operative to return a magnetic head to the position of a zero track independent of the track position sensor and the excitation condition of the stepping motor. For this reason, a current which is not under control of the system will flow in the FDD. When the system is powered on, there are instances where devices other than the FDD (e.g. a printer device, etc.) are to be operative while the FDD remains inoperative. But, in the case where a current which is not under control of the system flows through the FDD, the FDD remains operative and there is the possibility that power consumption of the entire system will exceed the power output of the battery. Excess consumption is most likely when plural sets of disk drive (multiple FDDs) are used.
Since the apparatus utilizing the ARTZ system cannot be employed in the battery-driven portable computer, it has been necessary to employ the above-mentioned apparatus with the provision of a stopper.